Hmmm...interesting... Since the Beta seems like it might launch tomorrow or Wed., I'll reserve my further questions until I've had a chance to actually see for myself how these interact. At the moment, using the alpha as a mask for the spec doesn't really seem to do much on its own other than adding variation to break up the tiling of the spec map (stage 5), since you can do major tweaks to the the spec map itself (in addition to its use in wet reflections). Which, I guess in and of itself IS quite a bit.

Am I right in guessing that most of these alpha maps tend to hover right around 50% gray, maybe a little less (i.e. if you were to average all of the pixels in the texture)?

It is a very effective way of breaking the tiling, yes. It is also useful if you want to highlight certain areas of the texture through the spec map (or the inverse).
Typically, the alpha channels for the ISI tracks are on the white side.

Ok, even though I said I was going to reserve my questions, I can't help but asking another---I've got so many!

Do the track reflections (reflectedenv?) have any sort of falloff depending on viewing angle? I remember one of the other guys around here always asking about proper Fresnel reflections... I'm sure it wouldn't matter much during a race, but it would probably make for some sweet-looking replays